It is a measure of just how far Alexis Sanchez’s star has fallen that neither the now rejuvenated club he left behind, nor the ailing team he was supposed to invigorate, will miss him when Arsenal renew hostilities with Manchester United at Old Trafford this evening.

Four places and eight points separated Jose Mourinho’s side from the remnants of Arsene Wenger’s crumbling empire when Sanchez was unveiled at Old Trafford, piano and all, last January.

Less than 12 months on and it is United staring up the table with envy, lagging behind and clinging to remote hopes of Champions League qualification.

It was a wholly different story back in February when United’s executive vice chairman Ed Woodward excitedly revealed that the enthusiasm generated by Sanchez’s signing saw United set a club record for shirt sales in January, three times the previous best.

An FA Cup semi-final goal against Tottenham aside, it remains the Chilean’s most noteworthy achievement since his move north.

United were confident they had pulled off a sensational Robin van Persie-esque coup by beating Manchester City to Sanchez’s signature, but their plan for the former Barcelona forward appears to have begun and ended with his showy unveiling.

Sanchez scored just once in his first 10 games as a United player, converting a rebound after his initial penalty had been saved by Huddersfield goalkeeper Jonas Lossl, and would add just two more goals in 15 subsequent games in all competitions as his season petered out, while City, even without Sergio Aguero for the run-in, powered to the Premier League title.

Despite the lack of an instant impact, Mourinho remained confident Sanchez’s initial were struggles were just those, teething troubles.

The rest of the United squad had been taken with the Chilean’s attitude and relentless pursuit of perfection, while the player himself had even asked to return early for pre-season training, recognising the need to hit the ground running in August.

Sanchez did impress on United’s troubled summer tour of America, during which Mourinho forecast the ‘difficult season’ that is playing out.

The 29-year-old has scored just once, the last minute winner against Newcastle which reportedly saved his manager’s job, in 12 games and looks almost completely spent.

Mourinho has trialled Sanchez through the middle in a bid to help him rediscover the explosive form he demonstrated when he was deployed as a central striker at the start of the 2016/17 season, but to no avail and the United faithful have grown all too accustomed to the sight of Sanchez dwelling on the ball, coughing up possession and disappearing up blind alleyways.

While none of those traits were particularly uncommon, even during the more productive spells of his Arsenal career, he was part of a side built to attack.

He has never been afforded the same freedom by Mourinho, whose defensive demands haven’t set well with a player who was indulged by his previous manager, and triggered a rapid decline in their relationship.

Fitness, too, has been an issue with his latest setback, a hamstring injury which will rule him out until the New Year, no surprise to sources at Carrington who have told Metro.co.uk that Sanchez has struggled to adapt to the change of emphasis in training.

At Arsenal he was used to far more ball work than at United, where much of the focus is on fitness and tactical organisation.

His emotional state took a further downturn following the break-up of his long-term relationship with Mayte Rodriguez in September and has appeared to be increasingly disenchanted with life in the north west.

He is said to have struggled to form close friendships with any of United’s first team squad, while the £350,000-a-week deal he signed in January has been a bone of contention for a number of his peers whose own contracts are up for renewal, particularly in the case of David de Gea, who is seeking parity before committing the peak years of his career to the club.

Arsenal, meanwhile, have emerged from the embarrassment of losing their star player for nothing a far more cohesive and rounded squad.

Henrikh Mkhitaryan has impressed only fleetingly after he swapped Old Trafford for the Emirates but with Pierre-Emerick Aubameyang, the club’s record signing, having replaced Sanchez’s goalscoring output, he has barely been missed at all.

It is doubtful, in any case, that he would have thrived under Unai Emery’s ultra-thorough management style.

Despite their increasingly prolific seasons, both Aubameyang and Alexandre Lacazette has spent a fair degree of time playing out of position or on the bench, while Aaron Ramsey and Mesut Ozil have found their reputations have counted for little when it comes to regular inclusion.

Whether Arsenal are able to record a first Premier League win at Old Trafford since 2006, despite their hosts’ dismal form, remains to be seen but that they are far better placed to do so without Sanchez as part of their attacking armoury only serves to emphasise his quite astonishing decline.